ELEMENTARY CONSTITUENTS OF THE FOOD OF PLANTS, 697 
decomposing the carbon dioxide taken up by them, and at the same time of setting 
free an equal volume of oxygen, in order to produce organic compounds out of 
the elements of carbon dioxide and water, or in other words to assimilate. It is 
very probable that under these circumstances carbon dioxide loses only one-half its 
oxygen, while the other half of the oxygen which is exhaled is derived from the 
decomposition of water. 
The fact is unquestionable — partly established by direct researches on vege- 
tation, partly inferred from the circumstances under which many plants live in a 
natural condition — that most plants which contain chlorophyll {e.g. our cereal crops, 
Beans, Tobacco, Sunflower, many saxicolous Lichens, Algae, and other water plants) 
obtain the entire quantity of their carbon by the decomposition of atmospheric 
carbon dioxide \ and require for their nutrition no other compound of carbon from 
without. But there are also plants which possess no chlorophyll and in which there- 
fore the means of decomposing carbon dioxide is wanting ; these must absorb the 
carbon necessary for their constitution in the form of other compounds. But since 
plants desdtute of chlorophyll are either parasites or saprophytes, they absorb their 
carbon in the form of organic compounds which have been produced by other 
plants that contain chlorophyll. Parasites draw these products of assimilation 
directly from their hosts, while saprophytes (as Neottia Nidus-avis^ Epipogium 
Gmelini, Corallorhiza innata, Afonoiropa, many Fungi, &c.) make use for the 
same purpose of the materials of other plants which are already in a state of 
decomposition. Even the food of Fungi which are parasitic in and on animals 
is derived from the products of assimilation of plants containing chlorophyll, 
inasmuch as the whole animal kingdom is dependent on them for its nutrition. 
The compound of carbon originally present on the earth is the dioxide, and the 
only abundantly active cause of its decomposition and of the combination of 
carbon with the elements of water is the cell containing chlorophyll. Hence all 
compounds of carbon of this kind, whether found in plants or in animals or in 
the products of their decomposition, are derived directly or indirectly from the 
organs of plants which contain chlorophyll. 
Hydrogen is present, equally with carbon, in every organic compound; in 
consequence however of the smallness of its combining equivalent, it falls far 
below it as a percentage constituent of the weight of the dried substance of 
plants. As has already been mentioned, the hydrogen of the plant is probably 
derived from the decomposition of water in cells containing chlorophyll in the 
presence of sunlight. It probably enters into combination with the carbonic 
oxide (CO) simultaneously presented to it by the reduction of the carbon dioxide^. 
^ [From the researches of Moll it appears that the roots take no part in supplying the plant 
with carbonic dioxide (Moll, Die Herkunft des Kohlenstoffs der Pflanzen, Arb. d. bot. Inst, in 
Würzburg, II. i, 1878).] 
2 [The abstract of Adolph Baeyer's paper on the Chemistry of Vegetable Life in Journ. Chem. 
Soc. 1871, pp. 331-341, should be consulted. It is shown to be probable that chlorophyll fixes 
carbon oxide just as haemoglobin does. When sunlight falls upon chlorophyll which is surrounded 
by carbon dioxide, that compound seems to suffer the same dissociation as at high temperatures, 
oxygen is liberated and carbon oxide remains combined with the chlorophyll. The simplest reduction 
of carbonic oxide is to formic aldehyde; it need only take up hydrogen, CO + H2 = COH2, and under 
the influence of the cell-contents, just as by the action of alkalies (which Butlerow has shown to be 
the case), the aldehyde is transformed into sugar.] 
